Method for working up aqueous residues from metallizing baths

Abstract

A method for purifying aqueous residues from exhausted metallizing baths, which contain at least one amino compound as a complex-forming agent, which comprises anodically treating the aqueous residue containing heavy metal ions and complex-forming agent at a voltage, current density and time sufficient to eliminate the complexing ability of the amino compound, and removing the heavy metal ions from said aqueous residue.

What is claimed as new and intended to be covered by Letters Patent is: 
     
       1. A method for purifying aqueous residues from exhausted metallizing baths, which contain at least one amino compound as a complex-forming agent, which comprises anodically treating the aqueous residue containing heavy metal ions and complex-forming agent at a voltage, current density and time sufficient to eliminate the complexing ability of the amino compound, and removing the heavy metal ions from said aqueous residue. 
     
     
       2. The method of claim 1, wherein said heavy metal ions are copper ions, and said amino compound is an alkalenediaminetetracarboxylic acid or salt thereof, wherein copper is deposited at the cathode during the anodic treatment. 
     
     
       3. The method of claim 2, wherein the pH of the aqueous residue subjected to electrolysis is alkaline at the start of the electrolysis and is then shifted to an acid pH by adding acid. 
     
     
       4. The method of claim 1, wherein, prior to the anodic treatment, the aqueous residue is freed from the predominant proportions of heavy metal ions and complex-forming agent by chemical precipitation. 
     
     
       5. The method of claim 4, wherein the aqueous residue is subjected to a first precipitation treatment, in which a predominant proportion of the heavy metal is removed, and to a second precipitation treatment, in which a predominant proportion of the amino compound serving as the complex-forming agent is removed. 
     
     
       6. The method of claim 5, wherein the heavy metal ions in the aqueous residue are predominantly copper ions, and the first precipitation comprises a forced chemical precipitation, by reductive treatment of the bath with particulate metallic copper at an alkaline pH and the precipitated copper is removed immediately after the end of said first precipitation. 
     
     
       7. The method of claim 5, wherein the complex-forming agent is ethylenediamine compound, in the form of the free acid or in the form of a salt, and said second precipitation comprises changing the pH value of the aqueous residue to the acid range to precipitate the predominant proportion of the ethylenediamine compound in solution, and the ethylenediamine compound precipitated is removed. 
     
     
       8. The method of claim 1, wherein the anodic treatment is an electrolysis at pH values of between 2 and 12 to convert the amino groups of the complex-forming agent to NO x  groups, in which x is a number from 1-2. 
     
     
       9. The method of claim 6, wherein at least 90% by weight of the amount of copper contained in the exhausted aqueous metallizing bath is removed in the first precipitation treatment. 
     
     
       10. The method of claim 7, wherein at least 90% by weight of the ethylenediamine compound present as the complex-forming agent in the exhausted aqueous bath is removed in the second precipitation treatment. 
     
     
       11. The method of claim 8, wherein the heavy metal ions still present in the aqueous residue after the precipitations are cathodically reduced and deposited during the electrolysis. 
     
     
       12. The method of claim 1, wherein the anodic treatment is an electrolysis at an anodic current density of at least 7 A/dm 2  and a cathodic current density of at least 2 A/dm 2 . 
     
     
       13. The method of claim 1, wherein said aqueous residues comprise an exhausted copper depositing bath for the preparation of printed circuits. 
     
     
       14. The method of claim 6, wherein said alkaline pH is a pH greater than 12. 
     
     
       15. The method of claim 7, wherein said ethylenediamine compound is ethylenediaminetetraacetic acid or salt thereof and said acid pH is less than 2.